As tensions with North Korea simmer, the U.S. military announced Wednesday that it has completed another successful test of its missile defense systems, but experts say the threats the nation now faces require a renewed commitment to more advanced anti-ballistic missile strategies.

According to the Missile Defense Agency, Tuesday’s test in the waters off the coast of Hawaii marked the second time an SM-6 missile fired from an Aegis warship successfully intercepted a medium-range ballistic missile target.

"We are working closely with the fleet to develop this important new capability, and this was a key milestone in giving our Aegis BMD ships an enhanced capability to defeat ballistic missiles in their terminal phase," MDA Director Lt. Gen. Sam Greaves said in a statement. "We will continue developing ballistic missile defense technologies to stay ahead of the threat as it evolves."

“For the defense of Japan, it’s extremely valuable and important because it improves confidence and reliability in capability to defeat medium-range missiles,” Riki Ellison, chairman and founder of the Missile Defense Advocacy Alliance, said.

Matthew Kroenig, a senior fellow at the Atlantic Council and a professor at Georgetown University, called it “quite significant” as a demonstration of the SM-6’s “promise for dealing with medium-range ballistic missile threats.”

According to Tom Karako, director of the Missile Defense Project at the Center for Strategic and International Studies, successful tests of these programs are fairly common, but the SM-6 missile has been approved for international sale, giving this particular test added significance.

“It could be purchased by some of our Asia-Pacific alliesso the context here is not merely of U.S. capability but also regional with partners and allies,” he said.

The Aegis BMD system is just one element of the nation’s missile defense capabilities. According to the MDA, there are four phases of a ballistic missile’s trajectory and each entails different challenges for interception: boost, ascent, midcourse, and terminal.

During the boost phase, a missile is easiest to detect but hardest to engage. The intercept window is less than five minutes and sensors must be relatively close to the launch site.

The midcourse phase, when a missile’s boosters burn out and it moves toward its target, can last longer and provide more opportunities for interception outside the earth’s atmosphere.

A ground-based system is in place in Alaska and California to counter attacks from enemies like North Korea or Iran midcourse, but it only works against intermediate and long-range missiles. The Aegis sea-based system defends against short- and medium-range attacks.

In the terminal phase, after the missile reenters the atmosphere, there is little time to intercept a warhead before it reaches its target. The Terminal High Altitude Area Defense (THAAD), the Aegis, and PATRIOT missiles are capable of terminal phase interception.

Various sea-based and land-based radar systems supporting operations and testing

Kroenig noted there are also opportunities to take out a missile prior to launch.

“First, so-called ‘left of launch’ attacks use cyber and electronic warfare to turn off the missile before it can even be launched,” he said. “Second, Washington could consider a pre-emptive strike, using our missiles to take out the enemy missile on the launch pad.”

According to the MDA, as of May 30, 2017, 76 of 93 hit-to-kill attempts had been successful across all programs since 2001. That includes 35 out of 42 Aegis tests and 13 of 13 THAAD tests.

Ground-based Midcourse Defense tests have a less impressive track record. The cost and the technology involved have limited the ability to try it out, but a successful test on May 30 was a notable milestone.

Government officials have expressed confidence in the strategic GMD system in place to protect the U.S. homeland from an ICBM attack, but Lauren Grego, a senior scientist at the Union of Concerned Scientists’ Global Security Program who studies that system, is skeptical.

“The evidence just doesn’t support that,” she said.

The ground-based midcourse system has succeeded in 10 of 18 tests since 1999, according to the MDA. Grego emphasized that those tests were conducted in “scripted for success” circumstances with no countermeasures and no decoys deployed to disrupt them.

“Those have not been tested under what we would consider operational conditions,” she said.

Kroenig also distinguished between the more reliable regional defenses that could protect allies and troops abroad and the system in place for the U.S. itself.

“The U.S. public is most interested in homeland ballistic missile defense,” he said. “For that, we have a system of 44 interceptors in California and Alaska. You can do the math. If a country like North Korea fires one or two missiles, we are in pretty good shape. If it launches a larger barrage, we are in trouble.”

Since the North Koreans know how many interceptors the U.S. has, Ellison predicted they would try to outmatch them if they ever did attack.

“You’ve got to address the lack of capacity we have right now for our homeland defense,” he said. “You’ve got to increase the capacity and the reliability.”

President Trump’s initial budget proposal for 2018 would have set missile defense spending $300 million below what Congress appropriated to the MDA in 2017, but amid rising concerns about North Korea earlier in August, Trump indicated that would change.

"We are going to be increasing our budget by many billions of dollars because of North Korea and other reasons having to do with the anti-missile," he told reporters at his golf resort in Bedminster, New Jersey. "As you know, we reduced it by 5 percent, but I've decided I don't want that. We are going to be increasing the anti-missiles by a substantial amount of billions of dollars."

Experts have offered mixed assessments of Trump’s predecessor’s handling of the issue, but they agree the issue needs to be a priority for the current administration.

According to Ellison, the Obama administration focused its missile defense development on regional systems like the one tested Tuesday, which at this point are highly reliable.

During his 2008 campaign, President Barack Obama complained about billions wasted on “unproven missile defense systems,” but once in office, he became more amenable to it. After scrapping a Bush-era plan for a Poland-based missile shield, he adopted a similar but smaller-scale project in the Mediterranean and Central Europe. The final stages of that effort were later canceled, though.

Following a round of North Korean missile tests in 2012, Obama ordered improvements to homeland and regional defenses. His administration also agreed to deploy a THAAD system in South Korea.

Obama never took significant steps to fund development of more advanced technologies for interception of ballistic missiles. He also halted development of laser-based interception technology that would have provided the ability to engage missiles in the boost phase.

Ellison was hesitant to second guess Obama’s priorities, saying the decisions were made based on perceived threats at the time.

“There could have been a lot more done, but it’s his administration’s prediction of what the threat was going to be,” he said.

Eight years ago, the Obama administration was not facing the same “missile-rich strategic environment” the U.S. and its allies now face, according to Karako.

“Where the threat is today, I think anybody occupying the White House would probably be doing more for both homeland and regional missile defense than the last administration,” he said, “but it’s about where the threat is.”

Kroenig is more overtly critical of the goal of “strategic stability” as laid out in the Obama administration’s 2010 Nuclear Posture Review.

“The strategic stability framework assumes that both sides' nuclear forces are part of the problem,” he said. “I am not worried about American missiles; I worry about the enemy. If we focus on deterrence and preventing the enemy from attacking, then we will have succeeded.”

Considering the nature of the current missile threat from North Korea and Iran, and potentially even Russia or China, experts see several potential areas for improvement if the increased funding Trump has promised for missile defense materializes.

“First, we should increase the number of deployed interceptors, up to around 100,” Kroenig said. “Second, we should develop multiple kill vehicles for the interceptors, giving each interceptor the chance to stop multiple incoming warheads. Third, we should add a third East Coast site in New York to expand coverage beyond the California and Alaska sites.”

According to Karako, there are plenty of steps that could be taken with each component of the defense system to increase their effectiveness. He cited space-based sensors and assets that can counter hypersonics and non-ballistic threats as options.

“There’s opportunity for block or incremental development for all four families of ballistic missile defense,” he said.

Ellison recommended focusing research on directed energy technology and air-based defense systems. As missiles become a cheap method for enemies to threaten the U.S., he said more frequent and extensive testing will be necessary.

“That’s where I think the friction will be with the critics,” he said, because those tests would require more money.

One area where he no longer expects to see friction is on the question of whether the U.S. should be developing an advanced missile defense system at all.

“I think the debate for having missile defense is over,” Ellison said. “Nobody would not want to have their country protected against the current and real threat that’s going to continue to proliferate.”